Embodiments relate to expandable particulates for use in subterranean applications and, in certain embodiments, to preparation of expandable particulates and their use in fracturing operations.
After a well bore is drilled, it may be necessary to fracture the subterranean formation to enhance hydrocarbon production. This may be particularly important in shale formations that typically have high-closure stresses. Access to the subterranean formation, in some instances, can be achieved by first creating an access conduit (e.g., perforation) from the well bore to the subterranean formation. Then, a fracturing fluid, called a pad, may be introduced at pressures exceeding those required to maintain matrix flow in the formation permeability to create or enhance at least one fracture that propagates from the well bore. The pad fluid may be followed by a fluid comprising a proppant in the form of a solid particulate to prop the fracture or fractures open after the pressure is reduced. In some formations (e.g., shale formations), the primary fracture can further branch into other fractures, smaller fractures, and microfractures; all extending through either a direct branch or indirect branch from the primary fracture and creating a complex fracture network. As used herein, a “complex fracture network” refers to a field or network of interconnecting fractures, which may include a primary fracture, secondary branch fractures, tertiary branch fractures, quaternary branch fractures, and the like. The complex fracture network encompasses the primary fracture and any and all branching fractures, regardless of size, man-made or otherwise, within a subterranean formation, that are in fluid communication with the access conduit and/or well bore. The proppant should hold the complex fracture network open, thereby allowing gas to flow through the complex fracture network to ultimately be produced at the surface.
The proppant may be selected based on its ability to maintain the fractures in a propped condition. This proppant characteristic may be based on the proppant size and crush strength, for example. The proppant may typically be an appropriate size to prop open the fractures while also allowing fluid to flow in between and around the proppant in the fractures. A variety of different materials have been used as proppant including silica (e.g., sand), walnut shells, sintered bauxite, glass, plastics, and ceramic materials, among others. While these materials have been used in fracturing operations, drawbacks have been encountered, especially in unconventional formations such as shale formations, where very small proppant has been used. For example, the very small proppant may have a tendency to settle to the bottom of the fracture and thus limit the size of the fracture after the pressure is reduced. Additionally, the smaller proppant may not have adequate strength to resist deformation/crushing upon application of the closure stress when the pressure is reduced.
In addition to proppant, swellable materials have also been deposited into one or more fractures as part of a fracturing treatment. Swellable materials may typically be capable of swelling upon contact with a swell-activating agent, such as water or a hydrocarbon fluid. While swellable materials have been included in fracturing treatments, because most materials that swell are typically soft, they may compress and expand outwardly into the fracture face upon release of pressure and effectively block/fill pore spaces. This may cause an undesired decrease in formation permeability. Thus, successful incorporation of swellable materials into fracturing treatments has been challenging.